1. Field of the Invention
The present invention relates to high security (anti-theft) constructions for fasteners, and particularly locking wheel nuts and wheel bolts used to secure vehicular wheels.
2. Description of the Prior Art
By way of background, locking wheel nuts and wheel bolts are commonly used to attach wheels to axle hub assemblies of automobiles and other vehicles. These fasteners are designed with security features that are intended to thwart theft by rendering the fasteners difficult to remove with conventional tools. In particular, the fasteners do not have the usual hexagonal head pattern found on conventional nuts and bolts, and instead have smooth cylindrical sidewalls that cannot be gripped by standard wrenches. Fastener removal requires the use of a special security tool having a unique key pattern that matches a corresponding groove pattern formed in the fastener end face.
Additional security can be obtained by fitting a free-spinning shroud over the security fastener's cylindrical sidewalls, such that the shroud is in concentric relationship therewith. The shroud discourages the use of theft devices that could otherwise be used to grip the sidewalls and remove the fastener without an authorized security tool. Because the shroud substantially surrounds all exposed surfaces of the sidewalls, no rotational purchase can be obtained on the fastener. The theft device can only engage the shroud, which freely spins under action of the theft device while the main body of the fastener remains stationary.
Commonly assigned U.S. Pat. Nos. 4,618,299, 4,726,723, 4,897,008, 5,112,176, 5,360,304, and 5,730,567 are directed to shrouded fastener designs of the foregoing type. The patented designs feature shrouds of various shape and size for both locking wheel nuts and wheel bolts. It is to such security fasteners that the present invention is directed. In particular, the present invention offers alternative security fastener constructions in which security shrouds are combined with locking wheel nuts and wheel bolts in a manner that minimizes design complexity and manufacturing expense while maintaining the requisite anti-theft characteristics.